The present invention relates to a giant magnetostrictive material and a heat treatment method for the giant magnetostrictive material and in particular to giant magnetostrictive material and a heat treatment method for the giant magnetostrictive material preferably applied to removal of working distortion of a giant magnetostrictive material and restoration of magnetostriction characteristics.
In recent years, a giant magnetostrictive material whose saturation magnetostriction is over 100 times that of traditional magnetic materials such as nickel and ferrite has been drawing attention in applications including actuators and sensors.
Among the RFe2 Laves intermetallic compounds as representative giant magnetostrictive materials (R is at least one kind of rare-earth element) TbFe2 has high magnetostriction when external magnetic field strength is high while it has lower magnetostriction when external magnetic field strength is low.
Thus, (Tb, Dy)Fe2 obtained by replacing part of Tb with Dy is in general use as a giant magnetostrictive material with higher magnetostriction in a low magnetic field strength.
In particular, a giant magnetostrictive material having a composition of Tb0.30Dy0.70Fe2.0 has a minimum crystal magnetic anisotropy at ordinary temperatures and large magnetostriction, and is greatly applicable and in widespread use.
The U.S. Patent Publication No. 4,849,034 discloses a method for improving the magnetostriction characteristics by applying heat treatment to RFex alloys such as Tb0.30Dy0.70Fe2.0 within a temperature range of 870° C. to 1100° C.
Heat treatment for removal of magnetostriction is performed within this temperature range because a fused phase releases a stress.
However, performing heat treatment on an RFex alloy at a temperature of 870° C. or above enhances fusing of an R-rich layer of the RFex alloy on a rod surface. Heat treatment on an a stack of a large number of RFex alloys in rod shape causes fusion of rods. Separation of rods is accompanied by mechanical distortion thus degrading the magnetostriction characteristics.